Different strategies have been used to convert an alkane species into alcohol. For example, a common strategy to convert methane into higher valued fuels is the gas-to-liquids (GTL) process of steam reforming methane into syngas (CO and H2) and subsequent reaction into methanol, but GTL requires large scales and billions in capital investment. This industrial pathway to convert methane into methanol involves two capital-intensive reactions: steam reforming and methanol synthesis. Steam reforming converts methane and water into hydrogen and carbon monoxide gases. This “syngas” is then fed into a methanol synthesis unit where the syngas is converted into methanol or other hydrocarbons. Several drawbacks exist for this industrial pathway. Firstly, the technical complexity is high. Two reaction units must be built as well as associated separations units afterwards. Numerous cryogenic separations and other utilities are needed to purify the syngas effluent from steam reforming to allow methanol synthesis to proceed efficiently. Auxiliary operations within the gas-to-liquids plants accounts for roughly half of the plant cost. Such technical complexity requires extremely large scale production facilities, thereby incurring high capital costs for gas-to-liquids plants. Secondly, steam reforming is energy intensive due to the high temperatures required (greater than 800° C.). Lastly, methanol synthesis requires high pressures (50-100 bar), incurring additional cost for compression pumps.
To avoid the large scale production facilities needed to make steam reforming and methanol synthesis profitable, alternatives have been researched for the direct partial oxidation of methane. One proposed alternative has been to utilize enzymes. An inherent problem with using enzymes industrially is their sensitivity to harsh temperatures and pH, difficulty of purifying large amounts of homogeneous enzyme, and difficulty in purification of alcohol products and enzyme from liquid water (solvent).
Inorganic catalysts for methane oxidation have been developed, but all suffer from at least one of the following deficiencies: expensive catalyst or oxidant, low selectivity, high temperatures, economic and/or energy inefficiency, or environmentally harmful reagents needed. Copper exchanged zeolites ZSM-5 and mordenite (MOR) have been studied for use in oxidizing methane at low temperatures (less than 423 K) using molecular oxygen. Yet, oxidized methane is strongly bound to the copper active site or Bronsted acid sites as a surface methoxy species, requiring water to extract methanol while simultaneously deactivating the active sites. Therefore, conversion of methane to methanol utilizing inorganic catalysts (e.g., zeolites) has heretofore been done stoichiometrically—with the production of methanol limited by the number of active sites for one cycle without the ability to sustain a continuous reaction process. Such a process would generally proceed as follows. The catalysts would be activated at a higher temperature. A flow of pure methane at a lower temperature would produce methoxy species at the active sites of the catalyst. Once the active sites of catalyst material were occupied by an oxidized methane molecule, an atmosphere of water would be introduced to extract this methoxy species as methanol. The deactivated catalyst would be dried and then heated to high temperatures to reactivate the catalyst. The multi-step cycle would then be repeated in order to extract a second set of stoichiometrically produced methanol. Such a process results in energy losses and lost time of unutilized catalyst during regeneration.
Accordingly, methods for catalytic alcohol (e.g., methanol) production are needed.